The design lane load is assumed to be distributed over a width of how many feet?

• A. 8 ft
• B. 12 ft
• C. 10 ft
• D. 14 ft

Answer: (C)

The main idea is that live-load from vehicles is not applied as a single point tip load but as a distributed influence over a finite deck width to reflect how the load spreads through the deck and into the supporting girders.

The design lane load is assumed to act over an effective width of ten feet. This convention provides a practical, standardized way to convert a vehicle’s load into a per-length load on a girder, capturing how the deck distributes forces without being as large as the full lane width or as small as just the tire contact. Ten feet is chosen as a balanced representation of the actual distribution, giving moments and shears that are realistic and consistently conservative for design.

If you used a wider width, the calculated moments would be smaller; with a narrower width, they would be larger. Ten feet hits a practical middle ground that aligns with typical deck behavior and code practice.